A Modularized Discharge-Type Balancing Topology for Series-Connected Super Capacitor String

Abstract

This paper proposed a modularized discharge-type topology for the voltage balance of series-connected super capacitor (SC) string. The proposed topology consists of cascaded converter modules and a boost converter. The cascaded converter modules discharge the higher voltage SCs directly with the ideal output current to realize a fast balancing speed and the boost converter feedbacks the extra energy from the higher voltage SCs to the super capacitor energy storage system (SCESS). The modular design of the cascaded converter modules makes the balancing system suitable for different voltage levels of SCESS. Unlike the charge-type topologies which discharge the higher voltage SCs indirectly, the proposed topology discharges the higher voltage SCs directly with a big current, and the over voltage phenomenon of SCs is then avoided, which means the reliability of the SCESS can be improved. The voltage stress of the switches inside the cascaded converter modules is low, which is different from the existing modularized discharge-type balancing topology. What is more, the control of cascaded converter modules and the boost converter can be implemented by analog devices which will simplify the control of the whole system. The control degree of freedom is high and the voltage of each cell can be controlled. An in-depth comparison analysis with the charge-type balancing topology is performed from the perspective of balancing speed and round-trip energy efficiency. The proposed topology and the balancing performance are confirmed by experimental results.